As a PR practitioner I have not had occasion to do crisis communications, even less respond to riots; but I would offer a few observations. Politicians and law enforcement would be well advised to study the 1991 riot in the Mount Pleasant neighborhood of Washington, DC. While initially the police were slow to recognize the significance of the disturbance, once they realized what they had on their hands their response was very intelligent.
The mayor met with the community, the chief of police went to the scene personally to take charge. This gave the police officers confidence that they would not be scapegoated for whatever happened. It was also a visible sign to the community that the their government was serious and not playing political games.
By meeting with community leaders Mayor Sharon Pratt Kelly drove a wedge between those with legitimate grievances that needed a response, and those who just like to loot. There is a lesson there and too often it is ignored.